This project consists of a systematic approach to investigate the structural information of the Tar chemoreceptor. The primary goal is elucidation of the fundamental mechanism of transmembrane signal transduction. The aspartate receptor is unique in that it has been well characterized which will allow our question to be approached. X-ray crystallography as well as electron microscopy will be used to resolve the structures of this receptor, with and without bound aspartate, at atomic resolution. Information from this study can be applied to other transduction receptors. Signal transduction is a phenomenon that occurs in all cell types. Bacterial chemotaxis and mammalian signal transduction both involve transmembrane signal transduction. Mutated forms of mammalian signal transduction proteins are often oncogenic. Therefore, a deeper understanding of the mechanisms of transmembrane signaling will lead to a better understanding of the events that cause cancer.